A85: Problems

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A85: Problems

Well, I was trying to write my first zshell program, but it didn't seem to
work right.  In fact, it doesn't work at all.  I was trying to display one
pixel, and by pressing the arrow keys it would move around.  But instead, a
bunch of boxes keep getting displayed, and the only way I can stop it is by
pressing 'on' twice.  The first press turns off the calculator, and the
second press turns it back on with all the weird characters on the screen
(but still operational).  Please help me correct my problem.  Here is the
asm file:

#include "TI-85.H"

	.org
	.db "Move around",0

init:

	ld a,4
	ld (5),a
	ld a,10
	ld ($800C),a
	ld ($800D),a

draw:
	ROM_CALL(CLEARLCD)
	ld a,($800C)
	ld b,a
	ld a,($800D)
	ld c,a
        CALL_(PlotPixel)    

key:

	call GET_KEY
	cp $04
	jp z,up
	cp $01
	jp z,down
	cp $02
	jp z,left
	cp $03
	jp z,right
	cp $37
	ret z
	jp nz,key

up:
	ld a,($800D)
	inc a
	ld ($800D),a
	jr draw

down:
	ld a,($800D)
	dec a
	ld ($800D),a
	jr draw

left:
	
	ld a,($800C)
	dec a
	ld ($800C),a
	jr draw

right:
	ld a,($800C)
	inc a
	ld ($800C),a
	jr draw

end:
	.end

PlotPixel:
  	 ROM_CALL(FIND_PIXEL)
        ld de,$FC00
        add hl,de
        or (HL)
        ld (HL),a
        ret
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